| 摘要 |
PROBLEM TO BE SOLVED: To enable arbitrary setting of a protecting voltage in both positive and negative directions, while holding cooperation with withstanding voltage of a circuit to be protected. SOLUTION: MOS transistors 28, 29 having parasitic diodes 28a, 29a are connected in series between signal lines 26, 27, in such a manner that their current flow directions are opposite to each other. In the case that positive static electricity infiltrates it and an input voltage Vin is increased exceeding a prescribed threshold voltage, a constant voltage circuit 41 is turned into a current flow state, and the MOS transistor 29 goes to ON state. At this time, a surge current flows via the diode 28a and the MOS transistor 29. In the case that negative static electricity infiltrates it and the input voltage Vin is decreased exceeding the prescribed threshold voltage, a constant-voltage circuit 36 is turned into a current flow state, and the MOS transistor 28 goes to ON state. At this time, a surge current flows via the diode 29a and the MOS transistor 28.
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